Numerical prediction on the effect of free surface vortex on intake flow characteristics for tidal power station

Abstract

For tidal power stations, the turbine operates under low-head near the free surface. The water levels change both the reservoir and sea sides, furthermore, the intake channel length is short. In this paper, the objective is to investigate the effect of surface vortices on operating conditions for tidal power units. Two-phase flows were simulated with a simplified reservoir model. The numerical method was verified with experimental data. In the reservoir model, the predicted surface vortex agreed well with various analytical models. From the numerical results, two-phase flows in the reservoir includes surface vortices sufficiently influenced the intake flows. It induces the non-uniformity of the pipe flow, which is by the strong vorticity and the air content in the water. The pipe entrance loss also directly influences operating conditions. Surface vortices influenced the net head and the flow rate passing through a pipe, and these effects increase exponentially as the water level decreases or the water level difference increases. Consequently, predicting the net head and the flow rate of the prototype could be complicated for site tests, and it would be also difficult to accurately predict prototype performances with the typical model test and numerical simulation methods for tidal power units.